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N. PETERS. PHOTO UTHOGRAPHEH AsmNsTO# D C (Model.)

Witqesses UNITED STATES PATENT OEEICE.

JOSEPH V. NICHOLS, OF BROOKLYN, ASSIGNOR TO THE UNITED STATES ELECTRICLIGHTING COMPANY, OF NEW YORK, N. Y.

ELECTRIC LAMP.

SPECIFICATION forming part of Letters Patent No. 236,833, dated January18, 1881.

Application filed October 18, 1850. '(Model.)

.To all whom t may concern:

Be it known that I, JOSEPH V. NIoHoLs, of the city of Brooklyn, countyof Kings, and State of New York, have invented certain new and usefulImprovements in Electric Lamps, of which the following is aspecification, reference being had to the accompanying drawing, whichforms a part hereof.

My invention relates to the class otl electric lampsknown asincandescentlam ps, in which light is produced by the incandescence ot'a continuous conductoroflow conductivity, forming a part oftheelectrical circuit of the lamp. WVhen the conductor is made of carbon,which has been found to be the most available Inaterial Jfor thatpurpose, it is essential that it should be effectually protected, whenhighly heated, from all access of oxygen, as it readily oxidizes at hightemperatures, and the incandescent part of the lamp has usually beeninclosed in a glass globe from which the air has been exhausted orexcluded. Various devices have been usedformakin g perfectly-tight joints about the conducting-wires; but sealing the glass of the globedirectly to the conductingwires has proved more effective and convenientfor this purpose than other constructions. Platinum has been consideredthe only available material ot' which to make the conductingwires inlamps so constructed, as the coefficients of expansion of other metalsdiffer considerably from that of glass, and glass, moreover, does notreadily adhere to them. The firm adhesion of the glass to the metal isobviously essential to a perfect joint, and, as the lamp undergoes veryconsiderable changes ot' temperature in use, any inequality in thecoefficient of expansion ot' the parts tends to separate them at thejoint or to crack the glass about the wires, and even with a metal ofthe same coefficient ofexpansion as the glass there is a considerabletendency to the formation of cracks in the glass about the wires, onaccount of the low thermal conductivity of glass. The platinum wire,becoming heated by conduction from the incandescent carbon, expandsrapidly, while the adjacent glass, conducting` the heat received fromthe platinum very feebly, expands slowly, and the glass is temporarilysubjected to a strain, which tends to crack it. The

use of platinum for conducting-wires in such lamps is, moreover,objectionable for other reasons. lts electrical conductivity iscomparatively low, and, as the leadingwvires have to be made quite smallwhen sealed into the glass, they are more or less heated by theirresistance to the current, and this aggravates the tendency to crack theglass due to the expansion caused by the heat received from the carbon.This metal, moreover, as is well known, has a remarkable capacity forabsorbing gases, and oxygen thus occluded in the conducting-wires isprobably, to some extent, given off again within the globe when thewires become heated, to the injury of the incandescent carbon, and theexpensiveness of platinum also adds considerably to the cost of thelamp.

It is obviously extremely desirable to use for conducting-wires a metalfree from these objections, such as copper, and to construct the globein such a manner as to avoid the tendency to the formation of cracksabout the wires.

I have found that by forming the base ofthe glass globe, or that partwhich immediately surrounds the comluct-ing-wires, ot' a compositionmade by mixing various metallic substances with silica and potash, theadhesion of the parts may be increased and the tendency to crackdiminished, and that when proper proportions are used the composition orcement so formed will readily adhere both to glass and to copper, andwill not crack when the parts are subjected to changes of temperature.The composition so formed is apparently metallovitreous in its nature,being, in fact, neither metal nor glass, but possessing for certainpurposes the properties of both. I find that a serviceable cement ofthis kind is formed by thoroughly mixing and fusing' together iiftyeightparts, by weight, of oxide of lead, seventeen parts of silica, ten ot'oxide of iron, ten of oxide of copper, and five ot'potash or soda. It isnot essential to use exactl I the ingredients named, or to combine themin precisely the proportions indicated; but it is essential that thecement should be rich in metallic constituents, and at the same timecontain sufficient silica to insure perfect adhesion to the glass of theglobe. I prefer to use the cementfor only ICO a small part of the baseof the globe immediately adjacent to the conducting-wires, and to formthe main part of the globe of glass.

The conducting-wires are made preferably of copper, on account of itshigh electrical conductivity and its cheapness; but other metals may beused, lif desirable.

The absence of cracks in the base of a lamp so constructed is probablydue to the assimi-` lation of the cement to the metal of the wires bothas regards its coefcient of expansion and as regards its thermalconductivity, and to its being more tough and elastic than glass. Theheating of the conducting-wires by the current is also largely avoidedby constructing them of metal of high electrical conductivity.

In the drawing I have shown a lamp constructed in accordance with myinvention.

A is the incandescent conductor. glass globe inclosing the conductor. GG are conducting-wires, of copper. D D are tubes, made of cement such asl have described, fused and sealed to the conductingwires at their upperends and to the glass of the globe at their lower ends, so that the baseof the globe is hermetically sealed about the conducting- Wires. Thetube of cement should be joined to the wire when both are at a whiteheat, so as to remove all oxide from the surface of the metal and insureperfect adhesion between the parts.

Bis al By way of additional precaution, a second joint may be madebetween the tube and the wire a short distance below the upper end ofthe tube.

The air may be exhausted from the globe in the usual way, so as to leaveas perfect a vacuum as practicable; or the air may be replaced with araretied atmosphere of hydrocarbon vapor or gas.

Havingthus described my invention, whatI claim as new, and desire tosecure by Letters Patent, is-

l. The combination, in an electric lamp, of a glass globe inclosing anincandescent conductor in a vacuum with conducting-wires connected withsaid conductor, and metallo-vitreous cement interposed between the glassof the globe and the conducting-wires and united to both by fusion,substantially as described.

2. ln an electric lamp, a glass globe inclosing the incandescent orlight-giving part in a vacuu1n,in combination with conductingwires ofcopper or other metal of high conductivity and metallo-vitreous cementinterposed between the glass of the globe and the conducting-wires andunited to both by fusion, substantially as described.

JOSEPH V. NICHOLS. iVitnesses S. F. RANDALL, HENRY HrcEL.

